A beech tree in the Knowledge garden at Ultuna has dark bleeding on the stem. Investigations showed that the disease is caused by the aggressive pathogen Phytophthora cactorum and more trees in the garden may be infected.
PhD student Miguel Angel Redondo discovered on a lunch walk that a beech tree at the Knowledge garden in Ultuna had dark bleeding on the stem, which suggest that stem canker may be present. In addition, the tree had less leaves than usual in the crown. With the consent of John Lööf Green who oversees the gardens, Miguel, the student Jérémy Martel, and researcher Jonàs Oliva started to investigate the infected beech as a part of a course in Forest Pathology held at the Department of Forest Mycology and Plant Pathology.
The group took samples that they analysed by growing them on agar plates. Then DNA from the colonies growing at the agar plates were extracted and analyzed. The DNA sequence perfectly matched a species called Phytophthora cactorum.
– At this point we were very concerned as Phytophthora cactorum is an aggressive species that can infect nearly 200 different plant species, including many fruit trees, says Jérémy Martel.
Phytophthora cactorum is often introduced along with infected living plants from nurseries, which is probably how it came to Ultuna. All species in the Phytophthora group infects and spreads via water and soil. The spores germinate when the conditions are right, this usually means warm temperatures and water in the soil.
– We think that actions should be taken to control the disease. The wide host range of this oomycete poses a problem to the gardens. Only one single tree has shown symptoms, but this does not mean that other trees has not been infected as well. There are different compunds that can be used to fight this disease; phenylamides and phosphonates. They suppress the pathogen and enhance the resistance of the infected tree, says Miguel Angel Redondo.
– This was a great opportunity to teach forest pathology with a real case study. It is of course extra interesting that the disease was discovered so closely, at the university campus! It was great to collaborate with the people managing the gardens in Ultuna. We really got the opportunity to benefit from each other expertise, says Jonàs Oliva.
Phytophthora cactorum has an extremely wide host range, and can infect over 200 species or 160 genera of trees, ornamentals, and fruit crops. In general, P. cactorum is capable of infecting both young and old plants, and causes root rot and crown defoliation of the many genera it infects. Read more about Phytophthora cactorum on Wikipedia.
jonas.oliva@slu.se, 018-671602